With development of touch technology, there are two main requirements for a touch screen, one is to increase the size of the touch screen with the development of display technology, and the other is to increase resolution of the touch screen due to an application such as handwriting recognition, gesture recognition, mapping and the like.
To improve the resolution of the touch screen, the most effective technique is to increase the number of infrared-receiving diodes, but this will bring difficulty to design and production of the touch screen. Moreover the increase in the number of elements means an increase in cost. In this method, due to the increase in the number of sensors, the response rate of the touch screen will certainly be affected.
Without increasing the number of infrared emitting and receiving diodes, the resolution can be improved through off-axis scanning (i.e., infrared light emitted by one infrared-emitting diode can be received by a plurality of infrared-receiving diodes), but such scanning greatly affects the response rate of the touch screen. Since it is necessary to perform an anti-interference light processing before detecting the signal of the infrared-receiving diodes, assuming that the response time of a first-stage processing circuit (for example, including a sampling holding circuit and an analog subtractor) to filter out the interfering light from the received signal of each infrared-receiving diode is t1, and the response time for switching operation of a multiplexer is t0, then in the case that there are one infrared-emitting diode and n (n≧2) infrared-receiving diodes, the total time is T0=nt1+(n−1)*t0, whereby the response rate is too small and the practical effect is poor.